N10-009 Network Security Practice Question
A security analyst discovers that an unauthorized device is sending forged ARP replies to poison the ARP caches of other devices on the network. Which security feature should be implemented on the switches to prevent this?
⚠ Common exam trap
CompTIA often tests the distinction between DHCP snooping (which builds the trust database) and Dynamic ARP Inspection (which uses that database to filter ARP traffic), leading candidates to mistakenly choose DHCP snooping as the direct solution for ARP spoofing.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Dynamic ARP Inspection
Dynamic ARP Inspection (DAI) validates ARP packets on a per-interface basis by intercepting all ARP requests and replies and verifying that they match entries in the DHCP snooping binding table. If an ARP reply contains a forged IP-to-MAC mapping, DAI drops the packet, preventing ARP cache poisoning. This directly stops the described attack where an unauthorized device sends forged ARP replies.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Port security
Why it's wrong here
Port security limits the number of MAC addresses on a port but does not validate ARP packets.
When this WOULD be correct
Port security would be correct in a scenario where the question asks how to prevent unauthorized devices from connecting to a switch port by limiting the number of MAC addresses allowed per port.
- ✗
DHCP snooping
Why it's wrong here
DHCP snooping filters DHCP messages and builds a binding table, but does not directly inspect ARP traffic.
When this WOULD be correct
A question asks: 'A user connects a rogue DHCP server to the network, assigning invalid IP addresses. Which switch feature should be enabled to block unauthorized DHCP server responses?' In that scenario, DHCP snooping is the correct answer.
- ✓
Dynamic ARP Inspection
Why this is correct
DAI uses the DHCP snooping binding table to validate ARP packets and drop spoofed ones.
- ✗
STP BPDU guard
Why it's wrong here
BPDU guard protects the spanning tree topology by shutting down ports that receive BPDUs.
When this WOULD be correct
A question asking which security feature prevents unauthorized switches from being connected to the network and causing STP topology changes, such as when a rogue switch sends superior BPDUs to become the root bridge.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓Dynamic ARP InspectionCorrect answer▾
Why this is correct
DAI uses the DHCP snooping binding table to validate ARP packets and drop spoofed ones.
✗Port securityWrong answer — click to see why▾
Why this is wrong here
Port security limits MAC addresses on a port but does not inspect ARP packets; it cannot prevent forged ARP replies that poison ARP caches.
★ When this WOULD be the correct answer
Port security would be correct in a scenario where the question asks how to prevent unauthorized devices from connecting to a switch port by limiting the number of MAC addresses allowed per port.
Why candidates choose this
Candidates may confuse port security with ARP inspection because both involve MAC addresses, but port security does not validate ARP packet content.
✗DHCP snoopingWrong answer — click to see why▾
Why this is wrong here
DHCP snooping prevents rogue DHCP servers and IP spoofing by filtering DHCP messages, but it does not inspect ARP packets. Forged ARP replies are mitigated by Dynamic ARP Inspection, which validates ARP packets against the DHCP snooping binding table.
★ When this WOULD be the correct answer
A question asks: 'A user connects a rogue DHCP server to the network, assigning invalid IP addresses. Which switch feature should be enabled to block unauthorized DHCP server responses?' In that scenario, DHCP snooping is the correct answer.
Why candidates choose this
Candidates may confuse DHCP snooping with Dynamic ARP Inspection because both rely on the same binding table and are often implemented together, leading to the mistaken belief that DHCP snooping alone can prevent ARP spoofing.
✗STP BPDU guardWrong answer — click to see why▾
Why this is wrong here
STP BPDU guard is used to prevent unauthorized switches from participating in Spanning Tree Protocol by disabling ports that receive BPDUs, but it does not prevent forged ARP replies or ARP cache poisoning.
★ When this WOULD be the correct answer
A question asking which security feature prevents unauthorized switches from being connected to the network and causing STP topology changes, such as when a rogue switch sends superior BPDUs to become the root bridge.
Why candidates choose this
Candidates may confuse BPDU guard with ARP inspection because both involve network security at Layer 2, or they might think that any 'guard' feature can prevent unauthorized devices from sending malicious frames.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
Go deeper
Related to this question
Learn chapter
Network Device Hardening
Key term
Security
Security in IT is the practice of protecting systems, networks, and data from unauthorized access, damage, or theft.
Key term
Dynamic ARP Inspection
Dynamic ARP Inspection is a security feature that validates ARP packets on a network to prevent man-in-the-middle attacks by ensuring that only legitimate ARP messages are forwarded.
About these practice questions
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.